Arctic Snow Depth, Ice Thickness, and Volume From ICESat-2 and Crynat-2: 2018-2021

Using ICESat-2 and CryoSat-2 freeboards, we examine the variability of monthly Arctic sea ice snow depth, thickness and volume between October 2018 and April 2021. For the 3 years, satellite-derived estimates captured a decrease in mean April snow depth (similar to 2.50 cm) and ice thickness (similar to 0.28 m) equivalent to an ice volume loss of similar to 12.5%. Results show greater thinning of multiyear ice with an end-of-season thickness in 2021 that is lower by similar to 16.1% (0.50 m), with negligible changes over first-year ice. For the period, sea ice thickness estimates using snow depth from climatology result in thicker ice (by up to similar to 0.22 m) with a smaller decrease in multiyear ice thickness (similar to 0.38 m). An 18-year satellite record, since the launch of ICESat, points to a loss of similar to 6,000 km(3) or one-third of the winter Arctic ice volume driven by decline in multiyear-ice coverage in the multi-decadal transition to a largely seasonal ice cover. Plain Language Summary Ice thickness and volume are critical variables for assessing the evolution and response of the polar sea ice cover to a warming climate. Retrieval of sea ice thickness from altimeter freeboards (i.e., the vertical height of the floating ice and snow above the local sea level) requires knowledge of loading due to snow. Until recently, snow depth has been prescribed with a climatology based on historical field records. Using freeboard differences from ICESat-2 and CryoSat-2, we are now able to derive snow depth estimates. In this paper we examine the differences between climatological and satellite-derived snow depth as well as the retrieved ice thicknesses from the two altimeter missions. Their changes for three winters between 2018 and 2021 are documented. Derived ice volume estimates are placed within the context of an 18-year satellite record.